This application claims the priority of German application number 198 58 740.6, filed Dec. 18, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a cutter head and to a knife and a knife holder, which can be used for such a cutter head. Preferred embodiments of the invention relate to chipper cutter heads for chip forming timber machining.
Cutter heads of this type fitted with one or more suitable knives are used, for example, for the removal, in the form of chips, of lateral segments of logs in profile chipping cutters and choppers for the manufacture of paper wood chips. On a rotating cutter head, peripheral knives are generally used as chipping knives and end knives as flat facing knives to form a corresponding chipping cutter system. Precise positioning of the knives is very important, especially in the case of flat facing cutters, which produce the final surface on boards and beams. To this end, conventional knives are often pre-adjusted in an appropriate adjusting device by means of adjusting screws fitted to the knife. Indexing the knives by appropriate shaping so that they can be fixed only in a certain position to the knife mounting area of the cutter head is known as an alternative. However, play due to the design thereof may lead to inaccuracies and hence to an unsatisfactory surface of the boards or beams. In addition to the knives with just one cutting edge that were once exclusively used, so-called reversible knives have been used increasingly in recent years, which are provided with a cutting edge on each of the opposite sides and which, once one cutting edge has become worn, can be fixed in a position turned through 180xc2x0 in order to use the other cutting edge on the cutter head. The knives are conventionally clamped against the knife mounting area and in this way retained there by means of clamping elements, which are screwed into the cutter head. Instead of rotary cutter heads that rotate in operation, fixed cutter heads fitted with knives can now also be used, to which the workpiece to be machined is advanced by rotational or other movement.
A cutter head of the said type for a profile chipping cutter with chipping knives and a circular saw annular element as smooth finishing tool is disclosed in German printed patent specification DE 195 13 699 C1.
In a cutter head of the generic type, as is disclosed in U.S. Pat. No. 5,271,440, reversible knives with plane knife contact surface and toothed profiling of the opposing knife front face are proposed. The knives are clamped against the knife mounting area of the cutter head by means of a clamping element, which is screwed on to the cutter head or a knife holder element thereof, and with a contact surface, which is provided with a corresponding, toothed surface profiling, are pressed against the toothed front surface.
In a type of cutter head, as is described in U.S. Pat. Nos. 4,997,018; 5,146,963; 5,271,442; 5,333,659; and 5,511,597, knives are used which in the central area of their contact side have a flat recess of rectangular cross-section. In this way the edge of the recess outwardly terminates essentially perpendicular to an adjoining free tool face of the knife. A corresponding key, formed on the knife mounting area, engages in the recess. A clamping element screwed on the cutter head or a knife holder element thereof presses against the knife front face remote from the holder, thereby clamping the knife to the knife mounting area.
In a further cutter head of the generic type, disclosed in the U.S. Pat. No. 5,348,065, knives are proposed which in cross-section comprise two edge areas with a parallel and angular offset and an intervening central area inclined in relation thereto. The central area abuts each edge area respectively at a V-shaped angle of more than 135xc2x0. As a result the knife, on each of the two opposing main surfaces, has two pairs of opposing, abutting V-shaped bearing surfaces, which interact with correspondingly V-shaped counter-bearing surfaces on the knife mounting area or on a clamping element, so that the knife is pressed by the clamping element and thereby clamped against the knife mounting area, interlocking therewith.
Common to all the above-mentioned, conventional cutter heads is the fact that the knife is held by a clamping element, which is fixed to the cutter head by one or more screw connections located at the side of the knife. Consequently only one side of the clamping element presses on the knife, so that the line of application of the clamping compressive force that the clamping element exerts on the knife runs laterally side by side with the line of application of the screw fixing of the clamping element.
In addition to a cutter head of the generic type in accordance with U.S. Pat. No. 5,348,065 cited above, the published German patent application DE 33 14 127 A1 also discloses a cutter head not of the generic type, in which the upper part of a filler element of a basic cutter head body forms a knife holder, on which an elevation of rectangular cross-section is formed, which engages in a corresponding rectangular recess in the knife. The knife and a closing plate arranged thereafter in the direction of rotation are each fixed to the knife holder from the top side by means of screws.
In a chopping device described in the German published patent application DE 24 56 034 A1 a knife of non-generic type is used, in which the knife comprises an elongated plate element of V-shaped cross-section, which terminates at an end face in the form of a V-shaped tip forming the knife cutting edge. A plurality of the said V-shaped knives with end face cutting edge are inserted into a corresponding stepped profile of support plates on the cutter head side. A clamping collet or a clamping head with corresponding V-shaped bearing surface is mounted on each knife and fixed to the basic cutter head body by means of a screw, the said collet being inserted through an opening in the knife formed as a slot for knife adjusting purposes.
The invention addresses the technical problem of providing a cutter head of the said type and knife and knife holder suitable therefor in such a way that the knife/knives can be held, self-centring and relatively free of play, on the knife mounting area, and can be changed relatively easily without costly adjustment operations.
The invention solves this problem by providing a cutter head assembly comprising a basic cutter head body with at least one knife mounting area having holder contact surfaces inclined in a V-shaped cross-section, and at least one knife detachably fixed to the respective knife mounting area by an assigned fixing structure, said at least one knife having a knife cutting edge on at least one of two opposite sides of the V-shaped cross section, said at least one knife having knife contact surfaces correspondingly inclined in a V-shaped cross-section and bearing against the holder contact surfaces inclined in a V-shape, wherein the fixing structure retains the knife at the knife mounting area with a retaining force acting between the contact surfaces inclined in a V-shape and hence between the two opposite sides of the knife.
In certain preferred embodiments of the invention, the corresponding bearing and contact surfaces between knife and knife mounting area are formed on the one hand by contact surfaces on the knife mounting area having a V-shaped incline in relation to one another, and on the other by contact surfaces on the knife having a correspondingly V-shaped incline in relation to one another, and the means of fixing for locating the knife on the knife mounting area retains the knife, which is provided with one, or in the case of the reversible knife, two opposing cutting edges running perpendicular to the cross-sectional plane, by means of a retaining force which characteristically acts on the knife in the area between the bearing surfaces inclined in a V-shape. The line of application of the said retaining force therefore lies in the angular range spanned by the bearing surfaces inclined in a V-shape, so that when locating the knife on the knife mounting area, the action of the retaining force results in self-centering of the knife. The centered knife position is at the same time clearly defined by the pair of interacting contact surfaces, inclined in a V-shape and lying opposite one another in relation to the line of application of the retaining force. The retaining force acting between the said pairs of interacting contact surfaces inclined in a V-shape, also results in a uniform distribution of forces over the contact surfaces and thereby all in all in a favorable, uniform action of the fixing force on the knife and the knife mounting area. These characteristic features of the knife mounting therefore ensure secure gripping of the knife free of play at the cutter head, even under load in chipping operations, and facilitate rapid mounting of the knife with high repeat accuracy of the knife position when inserting a new knife and with no costly adjustment operations.
In certain preferred embodiments of the invention, the means of fixing comprise a direct means of fixing without clamping elements, that is a means of fixing which connects the knife directly to the knife mounting area and which is formed, for example, by one or more screw connections. Since the direct means of fixing act on the knife itself and not on a clamping element clamping it, there is in this case no need for such a clamping element.
In a cutter head developed according to certain preferred embodiments of the invention, the contact surfaces terminate outwardly with the formation of a corresponding shoulder essentially perpendicular to an adjoining free tool face of the knife. This is very reliable in preventing the penetration of chips and dust particles between knife and knife holder.
In a cutter head developed according to certain preferred embodiments of the invention, the contact surfaces inclined in a V-shape enclose an angle of less than 130xc2x0 and owing to this comparatively steep V-angle produce a correspondingly reliable self-centring function.
In a cutter head developed according to certain preferred embodiments of the invention, the V-angle selected for the contact surfaces on the knife side is slightly flatter than for the corresponding contact surfaces of the knife mounting area. This has the effect that when fitting the knife its contact surfaces initially bear against the knife mounting area primarily on the outer end areas of the V-flanks and are then pressed, self-centring under the action of the means of fixing, into the V-shaped receiver formed by the contact surfaces of the knife mounting area. In the process the material of the knife and/or of the knife mounting area elastically yields very slightly to a corresponding extent. The angular difference between the Vshaped contact surfaces of the knife on the one hand and the knife mounting area on the other is selected so that the mounted knife, by way of the interacting V-shaped contact surfaces, bears against the knife mounting area with a contact pressure which is still sufficiently high at the end flanks of the V-contact surfaces to ensure a secure, gap-free bearing contact there and thereby to prevent any penetration of dust particles.
In a cutter head developed according to certain preferred embodiments of the invention, the two contact surfaces on the knife having a V-shaped incline towards one another and hence also those on the knife mounting area are inclined at the same angle to the line of application of the retaining force, by which the means of fixing retain knife at the knife mounting area. This symmetrical configuration of the contact surfaces in relation to the retaining force is conducive to a uniform distribution of forces and thereby to a secure grip of the knife at the knife mounting area and the self-centring function of the contact surfaces.
In a knife according to certain preferred embodiments of the invention, it is provided that, on that contact face to be applied against the knife mounting area of a cutter head, with knife contact surfaces having a V-shaped incline, such that the knife is suitable for fitting to the cutter head of the type referred to above.
In a knife holder according to certain preferred embodiments of the invention, the knife holder forms a separate component as a knife mounting area for receiving a knife and can be detachably fitted to the basic body of a cutter head of the type referred to above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.